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Neuroscience Week 1 > Olfaction and Taste > Flashcards

Olfaction and Taste Flashcards

1
Q

perspective

A
  • smell and taste are the least well understood of the special senses- combine with orosomatosensory combine to create perception of flavor although olfaction in the dominant component
  • both are critical for physiology of lower mammals- repro phys, food intake, social behavior
  • less critical in humans, impact on QOL
  • disorders can be profoundly distressing as well as harbingers of more general disease states
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2
Q

problem for analysis

A
  1. the olfactory system has the capacity to discriminate among literally millions of odorants including those never smelled before
  2. gustatory system also open ended in its capacity to discriminate among compounds
  3. both maintain this despite death of old receptor elements and recruitment of new
    - how do we maintain perceptual stability?
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3
Q

basic peripheral and central components

A
  1. receptor cells that transduce odorant stimuli are bona fide neurons
  2. cell bodies are in OE
  3. in humans the OE lies in the poesterodorsal part of the nasal cavity below the cribiform plate on the nasal septum and lateral nasal wall
  4. the OE neurons relay information via axonal projections through the cribiform plate to the OB
  5. OB is first relay in the sensory chain
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4
Q

pathways for olfactory processing

A
  • from receptors to bulb
  • to olfactory bulb targets
  • pyriform cortex, olfactory tuberle
  • amygdala-to orbitofrontal cortex (emotion), thalamus, hypothalamus (thalamus and OF cortex communicate
  • entorhinal cortex-to hippocampus-memories
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5
Q

OE

A
  • basal cells, neurons, supporting cells
  • neurons are bipolar with an apical dendrite ending in a knob with immotile cilia
  • each neuron has thin unmyelinated axon (C) that projects to bulb
  • cilia have OR
  • basal cells are self renewing and replace old sensory neurons- use old axon tracts
  • pseudostratified
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6
Q

neurogenesis in OE

A
  • basal cells continuously undergo mitotic division in a stem cell mode
  • sensory neurons life span 30 days
  • epithelial projections continually being broken down and re-forming
  • symmetric or asymmetric division, or can create 2 new neurons if needed
  • if no signal, dead
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7
Q

signal transduction in olfactory neurons

A
  1. odorant delivered to the epithelium along the airstream
  2. odorant diffuses through mucus to cilia
  3. odorant interacts with G coupled receptor protein, which increases cAMP and opens channels for Ca to flow in
  4. results in depolarizing receptor potential
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8
Q

diversity

A
  • 1000 ORs in humans
  • largest G grouped family in body
  • allows for lots of receptor types
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9
Q

generic olfactory receptor

A
  • 7 transmembrane domains

- aa seq homology

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10
Q

zonal distribution patterns

A
  • neurons expressing a particular OR are limited to a particular region
  • rodent-4
  • spatial pattern makes a code
  • ORs are slightly promiscuous
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11
Q

receptor expression patterns

A
  • underly coding
  • each neuron only has one receptor but that receptor isn’t finely tuned
  • within a zone, neurons expressing one type of OR can be homogeneously distributed or have a clustered distribution pattern
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12
Q

responses of olfactory neurons

A
  • single unit recordings show that they are broadly tuned
  • diversity of physiologically defined types of olfactory neurons parallels number of ORs
  • the OR on a neuron determines the responsiveness of that neuron
  • any one OR is broadly tuned to respond to a lot of different odorants that share a common molecular feature
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13
Q

spatial activity

A
  • each odorant has a unique pattern of spatial activity
  • there are inherent differences between areas of the epithelium and their response to odorants
  • these inherent differences reflect distribution of ORs
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14
Q

laminar organization

A
  • bulb is most rostral part of CNS
  • tubular in shape and the cells and their neuropil are arranged in concentric layers like an onion
  • glomerular, external plexiform, mitral cell, granule cell
  • mitral and tufted cells are the relay neurons that project to olfactory cortex
  • periglomuerular cells and granule cells are inhibitory interneurons that modulate activity of the mitral tufted cells
  • periglomerular are outmost shell of neurons
  • cluster around glomeruli
  • glomerulus is fundamental unit of anatomical and physiological organization in the bulb
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15
Q

projection of the epithelium onto olfactory bulb

A
  • not point to point
  • quadrant to quadrant
  • defined by boundaries of OR expression zones
  • dorsolateral zone projects to dorsolateral on bulb
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16
Q

distribution of specific or expressing neurons

A
  • one neuron has one OR type
  • within a zone, can be homogeneous or clustered
  • within a quadrant, axonal projections bring together the axon terminals of like neurons
  • all of the neurons expressing on OR converge onto the same set of glomeruli
  • pattern from epithelium to bulb creates spatial code for stimuli across bulb
17
Q

organization summary

A
  • one OR onto one glomerulus

- spatial patterns within and across zones

18
Q

step 1

A
  • glomerulus is both anatomical and functional
  • implied by connectivity
  • unique pattern of responsiveness of individual ORs and pattern of activation of the bulb
  • only maximally stimulate receptors send signals
  • granule cells can block
  • see picture
  • D is stimulated by C8-comes through when compiled C8 from A,B,C
  • glomeruli activated then mitral/tufted integrate
19
Q

step 2

A

-glomeruli are activated by odorants and different glomeruli by other odorants

20
Q

step 3

A
  • like immune system
  • each OR recognized odotope
  • different ORs recognize different odotopes even if molecule is relatively the same-OH vs not
  • one glomerulus is activated per odotope
  • odors are identified and discriminated by the overall activation of glomeruli across the whole bulb
21
Q

cranial nerves and taste

A
  • salt, sour, bitter, sweet, umami
  • VII-chorda tympani, ant 2/3 tongue, greater superficial petrosal to palate
  • IX-post 1/3
  • X-epiglottis
  • each axon innervates from 2-10 taste cells
  • gustatory axons innervate the NTS
22
Q

central taste projections

A
  1. the NTS has projections to the ventral posterior medial nucleus of the thalamus (VPM), hypothalamus, amygdala
  2. VPM, hypothalamus and amygdala project to the insula and the frontal cortex
23
Q

basic taste pathways

A
  • CN to NTS
  • to VPM of thalamus
  • NTS also to hypo and amygdala back and forht
  • VPM to insula and frontal cortex
  • connection to amygdala
24
Q

taste papillae

A
  • 4 fields- circumvallate, foliate, fungiform papillae, taste buds on soft palate
  • all taste fields respond to all tastants, but are more sensitive to some in certain areas
25
Q

trench and taste bud

A
  • papillas have trench around them with taste buds in trench
  • taste buds have many cell types
  • taste buds are pear shaped collections of cells surrounded by BL that are embeded in stratified squamous epithelium
  • each has 50-100 cells that include receptors and basal
  • taste receptor cells make synapses in periphery
  • microvilli of a taste cell extends through a taste pore
  • gustatory afferent axons synapse with receptor cells
  • stimuli cause depol with produce synaptic transmission across the receptor cell-axon synapse
26
Q

salt transduction

A
  • ionic
  • intracellular release in calcium and transmitter release
  • amiloride sensitive
27
Q

acids

A
  • hydrogen sensitive channels

- also ionic transduction mechanism which increases Ca and transmitter release

28
Q

sweet

A
  • G coupled
  • inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
  • T1R2 and T1R3
29
Q

umami

A
  • G coupled
  • inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
  • T1R1 and T1R3
30
Q

bitter

A
  • G coupled
  • inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
  • T2R
31
Q

across neuron

A
  • patterned reception
  • single axons respond to many different primary stimulus quantities although they will have a preferential maximal response to one
  • when recording from chorda tympani, differential firing pattern across pop-pattern
  • same group of axons can differentially encode the stimulus quality
32
Q

labeled line

A
  • banana receptor

- KO- lose all, but can restore singular functions

33
Q

Trigem

A
  • oral irritation
  • pungency
  • don’t use alcohol to test smell- trigem

Neuroscience Week 1 (11 decks)

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